To get an idea of the how the terrace fits with the mansard and dormer, here is a sketch I did to send to the company we might get the door and window onto the roof terrace from; I want a vertically pivoting window to go at the top of the stairs, I think. The flat roof really goes further back than this shows.
There is a lone tank stuck up there waiting to be moved, and the builders have told me again that our heating does things it ought not (bubble and steam, mainly! More to sort with the plumber who will probably pop by tomorrow; the staircase will arrive so that means they'll be taking away the bathroom wall and moving the door back, so they'll have to move the towel radiator in the bathroom, so he'll have to cap it off. They'll put in the first staircase and the rest of the hall floor around it and then they can work out how the steps up to the door onto the roof terrace will work! They're drawn on the wall but Big Dave says things like 'it'll be a bit, it'll be slightly, well you won't notice any difference; they're tricky but we've never got one wrong!
Note to self: check on phone, CAT 5 and aerial sockets before any plaster goes up!